The field of the disclosure relates generally to data transmission systems, and more particularly, to data transmission systems utilizing defect testing on in-service data transmission lines.
In conventional data transmission systems, two impedance mismatches can create an echo tunnel on a transmission line, such as a cable line. A receiver of the conventional system will then observe a resulting ripple in the frequency response from the transmission line, as well as a second impulse in the time domain response, which is normally delayed relative to a main impulse. However, when only one reflection is present, a resulting frequency response will be flat at the receiver (i.e., not attenuated), but have a relatively lower amplitude due to signal loss. It is therefore difficult, in conventional data transmission systems, to discover line defects, such as loose fittings and radial cracks, where an echo tunnel is not formed because only one impedance mismatch is encountered. This problem is rendered more difficult due to the fact that time domain reflectometers (TDR) cannot be used on in-service cable plant.
Accordingly, there is a need to be able to locate line defects on an in-service data transmission line when only one impedance mismatch is observed.